Conventionally, a check and control of air pressure of a tire mounted to a vehicle are desired for improvement of tire durability, improvement of wear resistance, improvement of fuel economy, or improvement of ride quality, and improvement of handling performance. For these purposes, various systems for monitoring tire pressure have been proposed. In such a system, in general, information about the air pressure of the tire mounted to a wheel is detected, a transmission device for transmitting the information is provided in a tire cavity area of each wheel, and the information of the air pressure of each tire is obtained from the transmission device to monitor the air pressure of the tire.
On the other hand, when a tire goes flat, a puncture repair agent to be injected into a tire cavity area located between the tire and a rim is often used. Because the puncture repair agent is a liquid, the agent adheres to the transmission device provided in the tire cavity area as well as a tire inner surface facing the tire cavity area when the agent is injected into the tire cavity area. In some cases, the agent becomes solidified to close an opening portion formed in the transmission device to affect measurement of the air pressure.
To cope with this problem, a wheel condition detection device capable of maintaining a normal detection condition by preventing entry of foreign matter through a communication portion for detection has been proposed (Japanese Patent Application Laid-Open No. 2008-62730).
To put it concretely, a TPMS (Tire Pressure Monitoring System) valve of the wheel condition detection device is provided with a communication portion opening and closing mechanism for opening and closing a communication hole formed in a housing. At the time of puncture repair, entry of the puncture repair agent into a detection space through the communication hole is prevented. This communication portion opening and closing mechanism is made up of mechanical bodies including a lid body and a torsion coil spring and automatically opens and closes the communication hole by centrifugal force acting on a wheel.
Moreover, there are proposed a tire pressure monitoring system and a tire pressure sensor unit for informing an occupant that tire pressure may drop after a punctured tire is fixed by using a tire puncture repair agent (Japanese Patent Application Laid-Open No. 2007-196834).
To put it concretely, the tire pressure monitoring system is provided to each tire of a vehicle and is provided with a sensor unit having a tire pressure sensor and a transmitter, a receiving device for receiving a radio wave from the sensor unit, and a control ECU for giving an alarm when the air pressure of each tire becomes lower than or equal to a threshold value. The system is provided with a puncture determination means for determining puncture of each tire and a puncture repair agent use determination means for determining whether or not the punctured tire was repaired by using the puncture repair agent after it was determined that the tire went flat. When it was determined that the punctured tire was repaired by using the puncture repair agent, the control ECU continues the alarm even if the tire pressure value from the air pressure sensor is a normal value.
Because the communication portion opening and closing mechanism of the device described in Japanese Patent Application Laid-Open No. 2008-62730 is made up of the mechanical bodies including the lid body and the torsion coil spring, the device itself is complicated and expensive.
In the system and the unit described in Japanese Patent Application Laid-Open No. 2007-196834, it is not certain whether or not the information about the tire pressure measured after the repair of the tire by using the puncture repair agent is correct. Therefore, it is impossible to determine whether a tire anomaly after the puncture repair is caused.